CN107406574A - Ultralow monomer polyurethane - Google Patents

Abstract

The present invention relates to the ultralow monomer PU prepolymers rolled into a ball comprising dissociateive NCO, and it can be obtained by polyalcohol, diisocyanate and NCO reactive compounds, and can be obtained by following steps：At least one polyalcohol is set to be reacted with least one polyisocyanates, wherein the polyurethane prepolymer that at least one polyisocyanates to be used relative to the amount of the hydroxyl molar excess of at least one polyalcohol, is rolled into a ball with acquisition containing free isocyanate groups；At least one compound with least one H acidic functionalities is added with into the polyurethane prepolymer containing free isocyanate groups group, and its amount make it that free isocyanate groups are rolled into a ball and the mol ratio (NCO of H acidic functionalities:XH ratios) it is 2~15, preferably 2.5~10, more preferably 3~8.Present invention also contemplates that the method for its preparation method, the laminating adhesive comprising the prepolymer, adhesive substrate and described adhesive are used for the purposes of laminated two or more film.

Description

Ultra Low Monomer Polyurethane

technical field

The present invention relates to ultra-low monomer polyurethane prepolymers comprising free NCO groups, obtainable from polyols, diisocyanates and NCO-reactive compounds; and to their preparation and their use.

Background technique

Laminating adhesives for bonding film-like substrates are generally known in the art and are widely used, for example, in packaging applications. They are solvent-containing or solvent-free, crosslinking or physically setting adhesives for bonding thin two-dimensional substrates such as plastic films, metal foils, textiles, paper or cardboard to each other. It is essential here that the adhesive bonding only slightly reduces the flexibility of the individual lamellae. The choice of individual film layers makes it possible to influence certain properties of these multilayer films, in particular permeability to water or other liquids, chemical resistance, permeability to oxygen or other gases.

Food products in solid form, pasty or liquid form may eg be packed in such packages. Everyday items such as plastic cutlery can also be packaged. Such packaging is also suitable for containing medical materials or items.

Adhesives based on reactive polyurethanes have proven to be particularly successful in practice. For example, DE 10 2004018048 describes PU adhesives which can be prepared based on PU prepolymers having terminal isocyanate groups. These prepolymers contain terminal isocyanate groups and can be used for adhesive bonding of films to produce multilayer composites.

The fields of application mentioned above mean that as little as possible migration of low molecular weight substances from the packaging into the packaging content should occur. These substances may be flavor-damaging substances or may have adverse health effects if ingested. In the case of films bonded with polyurethane, these substances may in particular comprise decomposition products from the isocyanate precursors used, for example from hydrolyzed polyisocyanates. Here, primary amines—in particular aromatic primary amines—can be formed from such polyisocyanate precursors. These substances are known to be harmful to health. Accordingly, there are various standards specifying the maximum content of such primary aromatic amines in films suitable for packaging.

It is conventional to use low molecular weight isocyanates in the synthesis of polyurethane adhesives. For chemical reasons it is not possible to prevent small proportions of monomeric isocyanates from also being present in the adhesive. In another group of polyurethane adhesives, oligomeric isocyanates are added to the adhesive to improve specific properties. They are intended to react with crosslinking agents such as polyols or with water to produce crosslinked adhesives. In this case, a certain proportion of oligomeric isocyanate remains in the adhesive after bonding. Such isocyanate groups are known to react when such objects are exposed to moisture during long-term storage, and since only a small proportion of isocyanate groups are present, these groups are then consumed by reaction to produce amino groups. Over time, this primary amine may then migrate into its surroundings. This is especially true in the case of low molecular weight hydrolysates.

These migrating substances are undesirable, especially in the field of packaging, in particular in food packaging. In order to avoid the disadvantages mentioned above, several technical solutions have been developed.

EP-A 0 118 065 proposes the preparation of polyurethane prepolymers in a two-stage process, wherein in a first stage a monocyclic diisocyanate is initially reacted with a polyfunctional alcohol and then in a second stage the diisocyanate is The prepolymer prepared in one step is reacted with the polyfunctional alcohol in excess of isocyanate. Mixtures prepared in this way have lower levels of monomeric isocyanate.

EP-A 0 150 444 relates to a process for the preparation of polyurethane prepolymers having a relatively low content of monomeric aromatic isocyanates. They are prepared by a process wherein, in a first reaction step, toluene-2,4-diisocyanate is reacted in the absence of other diisocyanates with polyols in an OH:NCO ratio of 4 to 0.55:1; And after almost all of the NCO groups with relatively high reactivity have reacted with some of the OH groups present, in a second reaction step, more NCO than toluene-2,4-diisocyanate in reaction step 1 Symmetrical bicyclic diisocyanate with higher group reactivity, its addition amount is equimolar or excess based on free OH groups, or based on the total amount of diisocyanate in steps 1 and 2 is 5 to 80% by weight, said The addition is optionally carried out at elevated temperatures and/or in the presence of customary catalysts. Although such known PU prepolymers have a low monomer content (ie according to the examples only 1 to 2.5%), in many cases they do not cure sufficiently fast.

EP-A 0 951 493 and the corresponding US granted patent US 6,515,164 B1 relate to low-monomer PU prepolymers containing free NCO groups obtainable from polyols and at least two diisocyanates differing in reactivity, characterized in that partly The ratio of NCO groups of the slower reacting diisocyanate to NCO groups of the faster reacting diisocyanate is greater than 6:1. Compared with those known from EP-A 0 150 444, the low-monomer PU prepolymers enable faster but sufficiently safe processing.

However, the known prepolymers still have the disadvantage that despite their low monomer concentration, they usually require a curing time of several days at room temperature to comply with food packaging regulations. Cure times are even longer if 1K systems are used (that is, such prepolymers are not combined with the hardener component at the time of use).

Contents of the invention

It is therefore an object of the present invention to provide an ultra-low monomer PU prepolymer containing free NCO groups which enables faster processing without compromising its adhesive properties, especially in food packaging applications with printing inks This is the case when used with the film. The ultra-low monomer PU prepolymer should be particularly suitable for the production of instantly food compliant laminates, so that there is no need to store the laminates and to make the laminates before further use in food packaging applications. The prepolymer undergoes a complete curing reaction. A high level of consumer safety should be provided before the ultra-low monomer PU prepolymer composition is fully cured, that is, it is desired to achieve compliance with EC10/2011 (Comission Regulation (EU) No 10/ 2011) stipulates that the primary aromatic amine (PAA) migration limit (migration limit) is less than 10ppb by weight. However, ultra-low monomer PU prepolymers should provide sufficient isocyanate content to obtain good adhesive properties. The prepolymers can be used in one-component systems (1K) and two-component systems (2K). Furthermore, the prepolymers should ensure a robust lamination process, that is to say that the laminate should comply with instant food standards even with varying mixing ratios of the two components.

In a first aspect, the present invention meets this object by providing a prepolymer composition comprising at least one polyurethane prepolymer containing free isocyanate groups, said polyurethane prepolymer being obtainable by the following steps:

(a) reacting at least one polyol with at least one polyisocyanate, wherein said at least one polyisocyanate is used in an amount such that NCO groups are present in a molar excess relative to the hydroxyl groups of said at least one polyol, to obtaining a polyurethane prepolymer containing free isocyanate groups; and

(b) adding at least one compound with at least one H-acidic functional group to the polyurethane prepolymer containing free isocyanate groups in step (a), in an amount such that the free isocyanate groups and the H-acidic functional group The molar ratio (NCO:XH ratio) is 2-15, preferably 2.5-10, more preferably 3-8.

In another aspect, the present invention relates to a method of preparing the prepolymer composition described herein, comprising:

(a) reacting at least one polyol with at least one polyisocyanate, wherein said at least one polyisocyanate is used in an amount such that NCO groups are present in a molar excess relative to the hydroxyl groups of said at least one polyol, to obtaining a polyurethane prepolymer containing free isocyanate groups; and

(b) adding at least one compound with at least one H-acidic functional group to the polyurethane prepolymer containing free isocyanate groups in step (a), in an amount such that the free isocyanate groups and the H-acidic functional group The molar ratio (NCO:XH ratio) is 2-15, preferably 2.5-10, more preferably 3-8.

In yet another aspect, the present invention relates to an adhesive composition comprising a prepolymer composition according to the present invention, optionally further comprising at least one tackifier, catalyst, stabilizer, crosslinker agent, viscosity modifier, filler, pigment, plasticizer, water scavenger (water scavenger) and/or antioxidant.

Another aspect of the present invention relates to a method of bonding two or more substrates selected from the group consisting of plastic surface articles, metals, fabrics, paper and cardboard, the method comprising:

(a) applying the adhesive composition described herein alone or in admixture with a hardener to the surface of at least one substrate to be bonded; and

(b) contacting the surfaces of the substrates to be bonded with the adhesive composition therebetween under conditions suitable to form an adhesive bond between the substrates; and

(c) optionally repeating steps (a) and (b);

Wherein the hardening agent preferably comprises an H-acidic functional group selected from hydroxyl, primary or secondary amino, mercapto or carboxyl; more preferably a polyol component; most preferably a polyol containing two or more hydroxyl groups per molecule components.

Another aspect of the invention relates to the multilayer laminate obtainable by the method according to the invention.

The present invention also encompasses the use of the adhesive composition described herein as a laminating adhesive, preferably as an adhesive for laminating at least two films, in particular as an adhesive for food packaging applications. The use of mixtures.

detailed description

As used herein, "one (species) or more (species)" refers to at least one (species) and includes 1, 2, 3, 4, 5, 6, 7, 8, 9 (species) of the above-mentioned species (species). Similarly, "at least one (species)" means one (species) or more (species), that is, 1, 2, 3, 4, 5, 6, 7, 8, 9 or more (species). "At least one" as used herein with respect to any component refers to the number of chemically distinct molecules, ie, the number of different types of the mentioned species, rather than the total number of molecules. For example, "at least one polyol" refers to the use of at least one type of molecule falling within the definition of polyol, but there may also be more than two different types of molecules falling within the definition, however it does not mean that only There is one molecule of said polyol.

"Laminated film" or "multilayer laminate" are used interchangeably herein to refer to two or more film layers, usually plastic films or metal foils, bonded together by a laminating adhesive. laminate.

In the present application, the term "film" refers to film-like substrates, ie thin two-dimensional substrates such as plastic films, metal foils, fabrics, paper and cardboard.

Unless expressly stated otherwise, references herein to molecular weights refer to the number-average molecular weight M _n . The number-average molecular weight _Mn can be calculated based on end group analysis (OH number according to DIN 53240) or can be determined by gel permeation chromatography according to DIN 55672 (in particular DIN 55672-1) with THF as eluent. If not stated otherwise, all given molecular weights are determined by gel permeation chromatography according to DIN 55672-1. The weight-average molecular weight _Mw can also be determined by GPC as described for _Mn .

In this context, if reference is made to OH value or OH content, said values or contents are generally those obtainable according to DIN 53240, where the figures obtained refer to the acetic acid used in the acetylation of 1 gram of a chemical substance containing free hydroxyl groups. and the number of milligrams of potassium hydroxide required.

The NCO content is determined according to Spiegelberger (EN ISO 11909) by titration with dibutylamine.

If not expressly stated otherwise, all percentages given herein with respect to compositions or formulations relate to % by weight relative to the total weight of the respective composition or formulation.

"About" or "approximately" used herein with a numerical value means ± 10%, preferably ± 5% of the numerical value. Thus, "about 70°C" means 70±7°C, preferably 70±3.5°C.

"NCO" as used herein refers to the isocyanate group -N=C=O. "NCO-terminated" as used herein relates to polyurethane prepolymers which contain at least one free NCO group at one end thereof.

If not expressly stated otherwise, primary aromatic amine (PAA) content or PAA migration limit refers to the amount of primary aromatic amine determined according to the test method described in Example 1 below.

The present invention is based on the surprising discovery of the inventors that the content of free isocyanate monomers can be further reduced by adding monofunctional compounds comprising NCO-reactive functional groups to polyurethane prepolymers, preferably low monomer polyurethane prepolymers, Products already bonded with the prepolymer, usually in the form of a laminating adhesive composition, can thus be used immediately for food packaging. This means that longer waiting times to ensure complete cure and the concomitant reduction in free isocyanate monomer content can be avoided. It is particularly surprising that a PAA migration limit of <10 ppb by weight according to EC 10/2011 (Commission Regulation (EU) No 10/2011) can be achieved directly after lamination. Furthermore, it was surprisingly found that the prepolymer compositions of the present invention exhibit improved adhesive properties compared to substantially NCO-free adhesives, such as silane-terminated polyurethane adhesives, especially at on printed film.

The polyurethane prepolymer of the present invention can be obtained by reacting at least one polyol with at least one polyisocyanate in step (a), wherein said at least one polyisocyanate is used in such an amount that the NCO groups are expressed relative to The hydroxyl groups of the at least one polyol are present in molar excess in order to obtain polyurethane prepolymers with free NCO groups, such as NCO-terminated PU prepolymers.

The at least one polyol may comprise a single polyol or preferably a mixture of two or more polyols. Suitable polyols are aliphatic and/or aromatic alcohols having 2 to 6, preferably 2 to 4 OH groups per molecule. The OH groups can be either primary or secondary OH groups.

Suitable aliphatic alcohols include, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8 - Octanediol and its higher homologues or isomers. Higher functionality alcohols are likewise suitable, for example glycerol, trimethylolpropane, pentaerythritol and the oligoethers of said substances.

Preference is given to using reaction products of low molecular weight polyfunctional alcohols with alkylene oxides as polyol components. The alkylene oxide preferably has 2 to 4 C atoms. For example, ethylene glycol, propylene glycol, isobutylene glycol, hexanediol, 4,4'-dihydroxydiphenylpropane or 4,4'-dihydroxydiphenylmethane with ethylene oxide, Propylene oxide or butylene oxide, or a reaction product of a mixture of two or more thereof. In addition, suitable polyfunctional alcohols (for example, glycerol, trimethylolethane or trimethylolpropane, pentaerythritol or sugar alcohol or a mixture of two or more thereof) form polyether polyols with the alkylene oxide Alcohol reaction products. Other polyols generally used for the purposes of the present invention are obtained by polymerization of tetrahydrofuran (poly-THF). Preferably polyalkylene glycol homopolymers or copolymers, preferably polypropylene glycol homopolymers or copolymers, polyethylene glycol homopolymers or copolymers, polytetramethylene glycol homopolymers or copolymers, or Polypropylene glycol/polyethylene glycol block copolymer. Especially preferred are polypropylene glycol homopolymers.

Polyethers which have been modified with vinyl polymers are likewise suitable as polyol components. Such products can be obtained, for example, by polymerizing styrene or acrylonitrile or mixtures thereof in the presence of polyethers.

Other suitable polyols are polyester polyols. Examples of these substances are obtained by combining low molecular weight alcohols - especially ethylene glycol, diethylene glycol, neopentyl glycol, hexanediol, butanediol, propylene glycol, glycerol or trimethylolpropane - with caprolactone Polyester polyol obtained by ester reaction.

Other suitable polyester polyols can be prepared by polycondensation. Such polyester polyols preferably comprise reaction products of polyfunctional (preferably difunctional) alcohols with polyfunctional (preferably difunctional and/or trifunctional) carboxylic acids or polycarboxylic anhydrides. Compounds suitable for the preparation of such polyester polyols are in particular hexanediol, 1,4-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol, 1,2,4-butanetriol, ethylene Glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, and polytetramethylene glycol. A certain proportion of trifunctional alcohols can also be added.

The polycarboxylic acid can be aliphatic, cycloaliphatic, aromatic or heterocyclic or both. They may be optionally substituted by, for example, alkyl, alkenyl, ether or halogen. Suitable polycarboxylic acids are, for example, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic acid, Acid anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimer fatty acid or trimer fatty acid, or a mixture of two or more thereof . Optionally, a certain proportion of tricarboxylic acid can also be added.

However, it is also possible to use polyester polyols of oleochemical origin. Such polyester polyols can be prepared, for example, by completely oxidizing epoxidized triglycerides comprising fatty mixtures of at least partially ethylenically unsaturated fatty acids and one or more alcohols having 1 to 12 C atoms. Ring opening and subsequent partial transesterification of triglyceride derivatives yields alkyl ester polyols having 1 to 12 C atoms in the alkyl residue. Other suitable oleochemical polyols are castor oil and dimer fatty alcohols (dimer glycols) and derivatives thereof. Castor oil is a triglyceride in which about 90% of the fatty acid residues are ricinoleate (12-hydroxy-9-cis-octadecenoic acid), and the remaining about 10% are mainly oleate and linoleate. Oleate. Dimer glycols can be prepared by dimerizing unsaturated fatty alcohols with basic alkaline earth metal compounds at temperatures above 280°C. They can also be obtained by hydrogenation of dimerized fatty acids and/or their esters. Another method of preparing dimerized diols involves dimerizing unsaturated alcohols in the presence of silica/alumina catalysts and basic alkali metal compounds.

Hydroxy-functional polybutadiene, such as that available under the tradename poly-BD, may also be used as the polyol for use in the compositions of the present invention.

Polyacetals are likewise suitable as polyol component. Polyacetals are taken to mean compounds obtainable from diols such as diethylene glycol or hexanediol or mixtures thereof, and formaldehyde. The polyacetals which can be used for the purposes of the present invention are likewise obtainable by polymerization of cyclic acetals.

Polycarbonates are also suitable as polyols. Polycarbonates can be formed, for example, by diols (e.g., propylene glycol, 1,4-butanediol or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol or two or more of them) mixture) with diaryl carbonate (for example, diphenyl carbonate) or phosgene reaction. Hydroxyesters of polylactones are likewise suitable. Another group of polyols may be OH-functional polyurethane polyols.

Polyacrylates carrying OH groups are likewise suitable as polyol components. These polyacrylates are obtainable, for example, by polymerization of ethylenically unsaturated monomers carrying OH groups. Ethylenically unsaturated carboxylic acids suitable for this purpose are, for example, acrylic acid, methacrylic acid, crotonic acid or maleic acid, or their esters with C ₁ -C ₂ alcohols. Corresponding esters carrying OH groups are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or methyl 3-hydroxypropyl acrylate, or a mixture of two or more of them.

The polyol and/or polyol mixture used is preferably liquid under SATP conditions, ie at 25° C. and a pressure of 1013 mbar.

The at least one polyisocyanate may be any suitable polyisocyanate, which means that any compound comprising at least two isocyanate groups is contemplated by the present invention. However, it is preferred that the polyisocyanate is a diisocyanate. Suitable diisocyanates include, but are not limited to, 1,5-naphthalene diisocyanate (NDI), 2,4'-diphenylmethane diisocyanate or 4,4'-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H12MDI ), xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI), dialkylene diphenylmethane diisocyanate and tetraalkylene diphenylmethane diisocyanate, 4,4 '-Dibenzyl diisocyanate, 1,3-phenylene diisocyanate or 1,4-phenylene diisocyanate, toluene diisocyanate (TDI), 1-methyl-2,4-diisocyanato ring Hexane, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 1-isocyanato Cyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI), tetramethoxybutane-1,4-diisocyanate, butane-1,4- Diisocyanate, hexane-1,6-diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane-1,4-diisocyanate, ethylene diisocyanate, methylene triphenyl triisocyanate (MIT ), phthalic acid-diisocyanatoethyl ester, trimethylhexamethylene diisocyanate, 1,4-diisocyanatobutane, 1,12-diisocyanatododecane and dimer fatty acid diisocyanate.

In various embodiments, the polyisocyanate used is selected from methylene diphenyl diisocyanate (MDI), toluene-2,4-diisocyanate (TDI), xylylene diisocyanate (XDI), hexamethylene Hydroxyl diisocyanate (HDI), polymeric diphenylmethane diisocyanate (PMDI), isophorone diisocyanate (IPDI), methylene-4,4-bis(cyclohexyl) diisocyanate (H12MDI) and mixtures thereof. Suitable polyisocyanates are available, for example, from Bayer AG (DE) under the trade name Commercially available.

The addition of small amounts of isocyanates with a functionality higher than 2, in particular triisocyanates, is also conceivable; and said addition can even be advantageous in certain cases. This triisocyanate can act as a crosslinking agent. At least trifunctional isocyanates are polyisocyanates formed by trimerization or oligomerization of diisocyanates, or by reaction of diisocyanates with low molecular weight polyfunctional hydroxyl- or amino-containing compounds. Commercially available examples are trimerization of the isocyanates HDI, MDI, TDI, XDI or IPDI, or adducts of diisocyanates and low molecular weight triols such as trimethylolpropane or glycerol. Further examples are the isocyanurates of hexamethylene diisocyanate (HDI) and of isophorone diisocyanate (IPDI).

In principle it is possible to use aliphatic, cycloaliphatic or aromatic isocyanates, but aromatic isocyanates are particularly suitable.

As noted above, in the polyurethane prepolymer forming reaction, the polyisocyanate is reacted at a concentration in excess of the stoichiometric concentration required for complete reaction with the hydroxyl groups. The excess used may comprise an OH/NCO equivalent ratio of 1:1.1 to 1:4, preferably 1:1.2 to 1:1.3. The OH content and the NCO content can be determined by titration as defined above.

In some embodiments, at least one polyol is a mixture of combined polyols, optionally combined with a solvent (eg, ethyl acetate); and heating the at least one polyol to about 30-95° C. , eg about 40-75° C., and optionally (in the absence of solvent) while stirring under vacuum to dry. After mixing, for the addition of the isocyanate, the temperature of the mixture may be set at about 40°C to 50°C, where the actual temperature is chosen according to the reactivity of the isocyanate added and taking into account the ensuing exothermic reaction. The polyol mixture can then be combined with at least one polyisocyanate in the reaction mixture to form a prepolymer. The prepolymer reaction is generally carried out at elevated temperature, preferably at about 60°C to about 95°C, more preferably at about 70°C to 85°C, for about 1 to about 24 hours. The reaction may be carried out in the presence of an added catalyst, wherein the catalyst is preferably a tin-based catalyst, more preferably dimethyldineodecanoatetin, eg Fomrez UL28. In a preferred embodiment of the invention, the reaction mixture contains no catalyst.

The reaction is continued until the free isocyanate content reaches or is very close to the calculated value determined by standard titration with dibutylamine (Spiegelberger, EN ISO 11909).

Preferred values for the free isocyanate content of the prepolymer composition after step (a) are 1 to 15% by weight, preferably 1 to 4% by weight, relative to the total amount of polyol and polyisocyanate in the mixture.

In general, polyurethane prepolymers containing NCO groups can be prepared in a known manner from the abovementioned polyols and polyisocyanates. Examples thereof are described in EP-A 951493 (US 6,515,164 B1 ), EP-A 1341832, EP-A 150444, EP-A1456265 and WO 2005/097861. Particular preference is given to low monomer PU prepolymers, such as those described in EP-A 951493 and EP-A150444.

As used herein, "low-monomer PU prepolymer" refers to a PU prepolymer or PU prepolymer comprising less than 1% by weight, preferably less than 0.5% by weight, of free isocyanate monomers (for example, the above-mentioned aromatic diisocyanates) as determined by GC or HPLC. PU prepolymer compositions/formulations.

Consistent with the methods described in EP-A 951493 and EP-A 150444, step (a) of the method described herein may comprise reacting at least one polyol with a first diisocyanate and a second diisocyanate, wherein the second A diisocyanate has at least one NCO group that is less reactive towards the hydroxyl groups of the at least one polyol than at least one of the NCO groups of the second diisocyanate. The reaction with the first diisocyanate and the second diisocyanate is preferably carried out sequentially, ie first the first diisocyanate is added and then the second diisocyanate is added. The point in time of addition of the second diisocyanate can be determined based on the free NCO content in the reaction mixture comprising the polyol and the first isocyanate (which can indicate the progress of the reaction, for example by using IR spectroscopy or titration methods, especially those described above). Sure. The first diisocyanate is preferably an unsymmetrical aromatic diisocyanate, such as 2,4-TDI; and/or the second diisocyanate is preferably a symmetrical aromatic diisocyanate, such as 4,4'-MDI. "Less reactivity" as used herein in reference to NCO groups means that a given NCO group is less reactive toward the hydroxyl groups of one or more polyols than another NCO group. For example, 2,4-TDI's unreactive properties after reaction of TDI with the hydroxyl groups of one or more polyols (where the NCO group at the 4-position reacts predominantly because it is more reactive than the NCO group at the 2-position) The reacted NCO group (usually the NCO-group in position 2) is less reactive than the NCO group of the added 4,4'-MDI. Thus, for example, when using an asymmetric diisocyanate with two isocyanate groups of different reactivity, the group with the higher reactivity will mainly react with the hydroxyl groups of the polyol, resulting in an unreacted, reacted less reactive free isocyanate groups. Due to their low reactivity, this unreacted NCO group does not readily react with the residual free hydroxyl groups in the polyol. When a second diisocyanate, preferably a symmetrical diisocyanate, is added, it has NCO groups that are more reactive than the remaining unreacted NCO groups of the first diisocyanate, so that these NCO groups of the second diisocyanate are now The groups will mainly react with residual free hydroxyl groups. As described in further detail in EP-A 951493 and EP-A 150444, this use of unsymmetrical diisocyanates and symmetrical diisocyanates with different reactivity of the NCO groups results in the reduction of residual unreacted diisocyanate monomers The content is lower.

Thus, in such embodiments, step (a) comprises a process wherein, in a first reaction step (step 1), a less reactive diisocyanate, preferably an asymmetric diisocyanate, such as toluene-2 , 4-diisocyanate (2,4-TDI)—reacts with at least one polyol in the absence of other diisocyanates, for example where the OH:NCO ratio is 4 to 0.55:1; and in almost all After the highly reactive NCO group (in the case of 2,4-TDI the NCO group at position 4) has reacted with some of the OH groups present, in a second reaction step (step 2), adding Symmetrical bicyclic diisocyanates (e.g. 4,4' -MDI), optionally added at higher temperatures and/or in the presence of typical catalysts.

A second diisocyanate (i.e., a symmetrical bicyclic diisocyanate) can be added in an amount of:

(a) an equimolar amount or excess based on free OH groups, or

(b) an amount of 5 to 80% by weight based on the total amount of diisocyanate in steps 1 and 2, or

(c) Less than equimolar amount based on free OH groups, for example, OH:NCO molar ratio is 1.1-12.

The OH and NCO group content can be determined as described above.

In various embodiments of this method, the molar ratio of NCO groups of the first diisocyanate to NCO groups of the second diisocyanate is at least 6:1, preferably at least 10:1, more preferably at least 15:1.

For other embodiments of this method, see EP-A 0 951 493 and EP-A 0 150 444, the entire contents of which are incorporated herein by reference, especially see EP-A 0 150 444, pp. 3-6 and Disclosure on pages 9-10 and WO 98/29466 A1 (corresponding to EP-A 0 951 493) on pages 2, 4-7.

The PU prepolymers thus obtained containing free isocyanate groups can be reacted in a further reaction step with other polyols, including triols or higher functional polyols. After this reaction, other polyisocyanates, such as triisocyanates or higher functional isocyanates, can be added to the resulting prepolymer composition.

The PU prepolymer obtained is then combined in step (b) of the process according to the invention with at least one compound having at least one H-acidic function comprising an active hydrogen atom. The amount of H-acidic functional groups refers to the amount of active hydrogen atoms according to the Zerewitinoff test described by Kohler et al. in Journal of the American Chemical Society, Vol. 49, p. 3181 (1927). At least one H-acidic function XH is an NCO-reactive function, where X is typically N, O or S. It may be a primary amino group, a secondary amino group, a mercapto group, a carboxyl group or a hydroxyl group, preferably a primary amino group, a secondary amino group or a mercapto group, most preferably a secondary amino group. In various preferred embodiments, the compound thus comprises at least one primary amino group, secondary amino group, mercapto group, carboxyl group or hydroxyl group as at least one H-acidic function. In some embodiments, the H-acidic functionality may also be an acidic C-H group, such as that present in malonate.

In a preferred embodiment, the compound having at least one H-acidic function is monofunctional with respect to said at least one H-acidic function. This means that compounds with at least one H-acidic function contain only one H-acidic function per molecule. According to the present invention, primary amino groups (NH ₂ ) are considered to be two H-acidic functions (XH), while secondary amino groups (NH), mercapto (SH), carboxyl (COOH) or hydroxyl groups (OH) are considered to have only one H-acidic function .

In various embodiments, at least one compound having at least one H-acidic function may comprise at least one silane group, preferably an alkoxysilane group. In various embodiments, the silane compound is a compound of formula (I)

((R ² ) _m (R ¹ O) _3-m Si-alkyl) _o Nu (I)

in

Nu is NH, _NH2 , SH, COOH or OH, preferably NH, _NH2 or SH, more preferably NH or SH, most preferably NH;

R _{is selected from H and C 1-20} ^alkyl , preferably C _1-4 alkyl, more preferably methyl and ethyl;

R ² is selected from C _1-4 alkyl, preferably methyl and ethyl;

m is 0, 1 or 2, preferably 0 or 1, more preferably 0;

"Alkyl" is linear or branched C _1-6 alkylene or C _3-6 cycloalkenyl (cycloalkenyl), preferably -(CH ₂ ) _n -, wherein n is an integer of 1 to 6, preferably 1 ~4, more preferably 1, 2 or 3; and

Wherein, o is 1 if Nu is NH ₂ , SH or OH, and o is 2 if Nu is NH.

Preference is given to aminosilanes comprising one or more alkoxysilane groups, preferably trialkoxysilane groups. Particularly preferred are bis(alkoxysilylalkyl)amines.

Exemplary compounds having alkoxysilane groups that may be used in the context of the present invention include, but are not limited to: 3-aminopropyltrimethoxysilane (AMMO), 3-aminopropyltriethoxysilane (AMEO) , 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (DAMO), N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-amino Ethyl)-3-aminopropylmethyldiethoxysilane, N,N-bis(2-aminoethyl)-3-aminopropyltrimethoxysilane, N,N-bis(2-aminoethyl) base)-3-aminopropyltriethoxysilane, N,N-bis(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-aminoethyl) Base)-3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-N'-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-( 2-aminoethyl)-N'-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-N'-(2-aminoethyl)- 3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-N'-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, bis(tri Ethoxysilylpropyl)amine, bis(trimethoxysilylpropyl)amine, N-(2-aminobutyl)-3-aminopropyltriethoxysilane, N-(2- Aminobutyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltriethoxy Silanes, and mixtures thereof.

Particularly preferred is bis(3-(triethoxysilyl)propyl)amine, available under the trade name 1122 (Evonik Industries) and Y-11699 (Momentive Performance Materials Inc.) is commercially available. The advantage of alkoxysilane compounds is that they act as adhesion promoters and increase the thermal stability and chemical resistance of the adhesive.

At least one compound having at least one H-acidic function is added in such an amount that the molar ratio of NCO groups to H-acidic functions (NCO:XH ratio=NCO/XH equivalent ratio, where X is usually N, O or S) is 2-15, preferably 2.5-10, more preferably 3-8.

By adding at least one compound having at least one H-acidic functional group which is reactive towards the NCO groups of the PU prepolymer, it is possible to reduce the Free monomeric isocyanate content. Furthermore, the prepolymer will be partially end-capped as the free NCO groups react with at least one compound having at least one H-acidic function. Particular preference is given to using compounds containing alkoxysilane groups, whereby the prepolymer is partially terminated with alkoxysilane groups. Since residual free isocyanate monomers cannot preclude reaction with H-acidic functions, a reduction in the overall monomer content is obtained while partially blocking the prepolymer with at least one compound having at least one H-acidic function. In various embodiments, the free monomers may comprise NCO groups that are more reactive towards H-acidic groups than the NCO-groups of the polyurethane prepolymer. This can further help to reduce the free isocyanate monomer content in the prepolymer composition.

The polyurethane prepolymers obtained after step (b) generally have an "ultra-low" monomeric polyisocyanate content of <0.1%, preferably <0.05% by weight, as determined by GC or HPLC. In various embodiments, when using TDI and MDI as described above, the isocyanate monomer content is about 0.05% TDI and <0.01% MDI and <0.01% other isocyanate monomers.

The resulting polyurethane prepolymers have isocyanate groups which are reactive toward OH groups or water. The free NCO content after step (b) is generally 1 to 5% by weight, preferably 1 to 4% by weight. The polyurethane prepolymers preferably have a molar mass (number-average molecular weight, determinable by gel permeation chromatography (GPC)) of 500 to 20,000 g/mol. The viscosity of the prepolymer at the adhesive application temperature in the temperature range of 20°C to 50°C should be 500 to 40,000 mPa·s as determined by the Brookfield test method (ISO 2555).

In some embodiments, triisocyanates or higher functional isocyanates may be added to the resulting prepolymer composition after step (b). Triisocyanates or higher functionality isocyanates such as oligomeric or polymeric MDI are generally less prone to migration than monomeric diisocyanates such as MDI or TDI. Thus, by adding triisocyanates or higher functional isocyanates, the NCO content can be increased, which in turn improves the adhesion properties, while the content of free monomeric diisocyanate can be kept low.

Adhesive compositions formulated using the prepolymer compositions described herein may also contain compounds having functional groups that are reactive with alcohols. In this case, it is preferred that the reaction between the alcohol and the reactive group of the selected compound is an addition reaction. Preferably, no low molecular weight species should be released in this reaction. Particularly suitable as functional groups are anhydrides of organic carboxylic acids. These anhydrides may be monomeric carboxylic anhydrides, especially those that are solid at 30° C., such as maleic anhydride (MA), phthalic anhydride, trimellitic anhydride or derivatives of these compounds. Oligomers of compounds containing more than one organic anhydride group may also be used. A particular embodiment uses polymers with anhydride groups having a molecular weight of greater than 1000 g/mol. Suitable polymers are known, especially those with MA groups. These substances can be incorporated into the corresponding polymers by copolymerization, but it is also possible to graft MA onto the polymers. Examples of suitable copolymers are copolymers of MA with styrene, vinyl acetate or (meth)acrylates. Examples of copolymers which can be grafted with MA are base polymers of polypropylene, polystyrene, polyester or polybutadiene. These substances can be grafted by known methods after their preparation in a polymer-analogous reaction with MA. The MA content in suitable polymers may vary from 3 mol % to about 60 mol % MA. According to the invention, it is advantageous if a relatively high proportion of MA is present in the polymer, in particular 10 to 55 mol % of MA. Particular preference is given to using MA-styrene copolymers, which have an MA content of 20 to 55 mol%, and which are preferably solid.

The amount of polymer or oligomer should be 1 to 20% by weight, especially 2 to 15% by weight, based on the adhesive composition. This amount can be chosen so that the amount of anhydride groups corresponds to the amount of alkoxy groups in the adhesive of the invention. Can also be used in excess. Any low molecular weight species carrying nucleophilic groups that may otherwise be present (eg amine-containing compounds) can also react with this component.

The polyurethane laminating adhesives described herein are 1K or 2K polyurethane adhesives, preferably 2K adhesives. The 1K polyurethane adhesive comprises the PU prepolymer with free NCO groups herein but no additional hardener, while the two-component polyurethane adhesive comprises the PU prepolymer with free NCO groups described herein with Further combinations of components (hardeners) comprising compounds containing at least two H-acidic functional groups. H-acidic functional groups include hydroxyl, primary or secondary amino groups, mercapto or carboxyl groups. This additional component is preferably a polyol component, ie a component comprising a polyol having two or more hydroxyl groups per molecule.

1K PU adhesives typically contain one or more of the NCO-functional polyurethane prepolymers described herein. These substances are usually crosslinked in the presence of water which is provided as part of the substrate to be bonded or from the air. The 2K PU adhesive contains an adhesive component comprising the above-mentioned PU prepolymer and a hardener component. Immediately before use, the two components are mixed and the resulting mixture must be processed before it is fully cured. The hardener component generally comprises a compound as defined above containing at least two H-acidic functional groups. The curing of the polyurethane adhesives according to the invention is therefore based either on the reaction of the NCO groups with reactive H-acidic functions (2K system) or on the formation of NCO groups with moisture from the applied adhesive, the substrate or the environment. Reaction of urea groups (1K system). If the at least one compound having at least one H-acidic functional group of step (b) contains at least one silane group, the curing of the adhesive can be further hindered by the interaction of the silane group from the applied adhesive, the substrate or the environment. The moisture forms the reaction support of the siloxane groups. To speed up this reaction, a catalyst, such as an amine or tin catalyst, may be present in the binder.

In some embodiments, the hardener includes an OH terminated polyester hardener. Such polyester-based hardeners are known in the art and can be obtained, for example, by reacting dicarboxylic acids with polyols in a polycondensation reaction. The dicarboxylic acids may be aliphatic, cycloaliphatic or aromatic and/or derivatives thereof (eg anhydrides, esters or acid chlorides). Specific examples of these substances are succinic, glutaric, adipic, pimelic, suberic, azelaic or sebacic acids, phthalic, isophthalic, terephthalic, Triacids, phthalic anhydride, tetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimerized fatty acids, and dimethyl terephthalate. Examples of suitable polyols are monoethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 3-methylpentane-1,5-diol, neopentyl glycol (2,2-Dimethyl-1,3-propanediol), 1,6-hexanediol, 1,8-octanediol, cyclohexanedimethanol, 2-methylpropane-1,3-diol , diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, dibutylene glycol, tributylene glycol, tetrabutylene glycol, and polytetramethylene glycol alcohol. Alternatively, they can be obtained by ring-opening polymerization of cyclic esters, preferably ε-caprolactone.

In a preferred embodiment, the polyesters are adipic, isophthalic, pimelic, suberic, azelaic and/or sebacic with neopentyl glycol, 1,4-butanediol, diethylene glycol, A polyester of any one or more of diol, 1,6-hexanediol, and 1,2-propanediol. In a preferred embodiment, the polyester hardener comprises adipic acid and/or isophthalic acid with any of neopentyl glycol, diethylene glycol, 1,6-hexanediol and 1,2-propanediol or A plurality of at least one hydroxyl terminated polyester.

In other embodiments, the hardener component may comprise one or more monomeric polyols. Suitable polyols are aliphatic and/or aromatic alcohols having 2 to 6, preferably 2 to 4 OH groups per molecule. The OH groups can be primary and secondary OH groups. Suitable aliphatic alcohols include, for example: ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8- Octanediol and higher homologues or isomers. Also suitable are higher alcohols, such as glycerol, trimethylolpropane, pentaerythritol. It is also possible to use the oligomeric ethers of the substances mentioned.

Other suitable hardener components include polyacetals, OH functional polyurethane polyols, and the like. Any two or more of the above-mentioned hydroxy-functional hardener components may also be used in combination.

The polyurethane adhesive composition may preferably be formulated as a laminating adhesive composition. The polyurethane adhesive composition can be formulated with further auxiliary substances likewise known per se to form laminating adhesives. Such substances include, by way of non-limitation and by way of example only: resins (tackifiers), catalysts (e.g. based on organometallic compounds or tertiary amines, such as based on tin compounds or DABCO), stabilizers, crosslinkers, viscosity modifiers additives, fillers, pigments, plasticizers, water scavengers and antioxidants. In embodiments of the 2K composition, these compounds may be included in the binder and/or hardener components.

Preferably, the polyurethane adhesives according to the invention are liquid at the application temperature, so that they can be applied in liquid form in the process for producing multilayer films. It is particularly preferred that the polyurethane adhesives according to the invention are liquid at room temperature, but hotmelt adhesives which melt only at elevated temperatures, for example temperatures above 100° C., are also conceivable.

The adhesives described herein may contain solvents or may be solvent-free. Suitable solvents are customary organic solvents which can evaporate at temperatures not higher than 130°C, in particular with boiling points below 100°C. The solvent may be selected from aliphatic hydrocarbons, aromatic hydrocarbons, ketones or esters. Solvents are used to reduce and adjust viscosity. The proportion of solvent relative to the total weight of the adhesive can vary within wide ranges, for example from 19 to 75% by weight. The adhesive used may also be solvent-free, ie not more than 5% by weight, preferably not more than 1% by weight, most preferably not more than 0.1% by weight of organic solvents. However, solvent-containing adhesives are preferred.

The adhesives described herein can be applied to the substrates to be bonded with all customary devices for adhesive application and with all known application methods (for example by spraying, coating, roller applicators, etc.). materials, especially films. After application, the substrates to be bonded are bonded together in a known manner. It is practical to apply the adhesive at elevated temperatures (eg, temperatures not higher than 120°C) to achieve better application and faster crosslinking reactions. However, the adhesives described here already exhibit good curing properties at room temperature or only at slightly elevated temperatures (eg 40° C.).

The prepolymers and adhesive compositions of the invention are suitable as such, or for their use in bonding plastics, metals, paper and cardboard (but especially for laminating fabrics, plastic films, metal foils, preferably aluminum foils) The form of a solution in an organic solvent is suitable. Conventional hardeners such as relatively high molecular weight polyols can be added (two-component systems) and surfaces with a defined moisture content can be bonded directly by using the products according to the invention. The film laminates produced with the products according to the invention are distinguished by high process safety during production at elevated temperatures. This may be due to the greatly reduced content of migratable low molecular weight products in the prepolymer. Furthermore, the prepolymers of the invention can also be used as primers for extrusion, printing and metallization and for heat sealing.

In various embodiments, the polyurethane laminating adhesives described herein can be used in known processes for bonding polymer-based and metal foils, especially aluminum foils, and films of paper, cardboard, and textiles, the polymers being Examples are polypropylene (PP), oriented polypropylene (OPP), polyethylene (PE), polyesters such as polyethylene terephthalate (PET), cellulose films, polyamides such as nylon (especially oriented poly amide (OPA) or biaxially oriented polyamide (BOPA)).

To form a multilayer laminate, the adhesive is applied to one or both, preferably only one, of the films to be bonded. The film may be a pretreated and/or printed film, for example an ink printed film. The application can be carried out at elevated temperature in order to obtain a thin and uniform coating. A second film of the same or different material is then laminated, usually under pressure. By repeating the lamination steps, laminates consisting of more than two layers can be obtained. The adhesive is cured and a multilayer film is obtained in which two films are bonded to each other. Curing can also be performed at elevated temperatures.

Accordingly, the present invention also relates to a method of bonding two or more substrates selected from the group consisting of plastic surface articles, metals, fabrics, paper and cardboard, said method comprising:

(a) applying a prepolymer composition or an adhesive composition as described herein, alone or in admixture with a hardener, to at least one surface of a substrate to be bonded; and

(b) contacting the surfaces of the substrates to be bonded with the adhesive composition therebetween under conditions suitable to form an adhesive bond between the substrates; and

(c) In case more than two substrates are to be bonded, steps (a) and (b) are repeated.

As detailed above, in a preferred embodiment at least one substrate, preferably two or more substrates, is a film-like substrate, preferably selected from plastic films and metal foils.

The invention also encompasses the multilayer laminates obtained by the process described, preferably bilayer laminates in which two film layers are bonded to each other by means of the abovementioned adhesives. The multilayer laminate may be a laminate for food packaging applications.

Furthermore, the present invention also relates to the use of the above-mentioned adhesive as a lamination adhesive, in particular as a lamination adhesive for laminating at least two film-like substrates, even more particularly for food packaging Use of the applied lamination adhesive. The film-form substrate may be those defined above with respect to the disclosed method.

Lamination adhesives are preferably used in order to achieve a PAA migration limit of <10 ppb by weight according to EC 10/2011 (Commission Regulation (EU) No 10/2011 ) directly after lamination.

It will of course be understood that all embodiments disclosed above in connection with the prepolymer composition of the present invention apply analogously to the adhesive composition, method, laminate and use of the present invention and vice versa.

The invention is further illustrated, but not limited, by the following examples. Wherein, unless otherwise stated, the indicated amounts are by weight.

Example

Embodiment 1 (the present invention)

In a three-necked flask equipped with a stirrer, a thermometer and a condenser, 1067.4g of PES 218 (OH value: 133mgKOH/g), 673.58g of PES 231 (OH value: 108mgKOH/g), 350.3g of polypropylene glycol (OH Value: 113 mg KOH/g), 350.0 g of polypropylene glycol (OH value: 236 mg KOH/g), and 873.7 g of ethyl acetate were mixed with 735.2 g of toluene-2,4-diisocyanate, and the resulting mixture was heated at 50°C. Due to the exothermic reaction, the temperature was raised and maintained at 80° C. until the NCO content measured by titration was only 3.85% by weight. After addition of 4,4'-diphenylmethane diisocyanate (4,4'-MDI), the reaction mixture was stirred at 80° C. for 3 hours, after which the NCO content was determined to be 3.05%. 249.2 g of PES 231 (OH value: 108 mg KOH/g) and 18 g of trimethylolpropane (OH value: 1254 mg KOH/g) were added, and the solution was stirred at the same temperature until the NCO content was 2.08% by weight. Add 716g ethyl acetate and 243.2g L75 (polyisocyanate based on 2,4-TDI or triisocyanate based on TDI, NCO value: 13.3% by weight) until a measured NCO content of 2.2% by weight.

Then the prepolymer was mixed with 1122 (bis(3-(triethoxysilyl)propyl)amine) was reacted with an NCO/NH equivalent ratio equal to 7.3:1. The resulting product had an NCO content of 1.94% by weight, a viscosity of 1510 mPa·s (measured three days after preparation, Brookfield/spindle 3/30 rpm), final 70% solids, and 0.05% by weight of 2,4-TDI and < An isocyanate monomer concentration of 0.01% by weight of 4,4'-MDI. No other isocyanate monomers were detected (<0.01% by weight).

The modified prepolymer and Hardener LA6152 (Henkel AG & Co. KGaA; OH component; solids content: 100% by weight) was used in combination as a 1K or 2K binder in a mixing ratio of 25:1 (NCO/OH equivalent ratio of 1.65:1) to obtain ^A dry coat weight of 3.5 g/m2 laminated the different film structures.

Laminate adhesion was tested by using a universal tensile testing machine with a synchronous recorder. The force range is 10-50N, and it is adjusted according to the expected adhesion level. 15 mm wide strips were prepared by using a strip cutter. Separate the strips slightly before clamping them. The peeling rate is 100 mm/min, the peeling angle is 90°, and the peeling length is 5 to 10 cm according to the range of fluctuation. The result was expressed in N/15 mm as lamination adhesion (adhesion strength-BS), and the separation pattern (% of ink transferred) was visually evaluated.

Table 1: Properties of printed OPP/OPP ink binders: NC-PU (gravure printed)

Table 2: Properties of printed OPP/OPP ink binders: NC-PU (flexo-printed)

color BS – 1 day BS – 14 days BS – 28 days blue 3.25/coexist tear 4.97/coexist tear 4.41/coexist tear blue White 1.99/0% ink transfer 4.35/coexist tear 3.57/90% ink transfer White 1.87/coexist tear 5.99/coexist tear 2.09/coexist tear

Table 3: Properties of printed PET/PE ink binders: PUR (flexo-printed)

color BS – 1 day BS – 14 days BS – 28 days blue 2.35/0% ink transfer 3.07/PET tearing 3.26/PET tearing blue White 2.23/0% ink transfer 3.94/PET tear 4.42/PET tearing White 2.52/0% ink transfer 1.33/100% ink transfer 1.59/100% ink transfer

Primary aromatic amine (PAA) migration was immediately evaluated on freshly laminated OPA/PE structures coated with 3.8 g/ ^m2 of prepolymer as a 1K adhesive. Migration tests were carried out by placing the laminate in a migration cell and covering 1 dm ² (from the PE side) with 100 ml of 3% by weight acetic acid for 1 hour at 70°C. The migrated solution was then analyzed after enrichment by HPLC with a PDA detector to detect 2,4-TDA, 2,6-TDA, 2,2'-MDA, 2,4'-MDA and 4,4' -MDA. The test results were <10 ppb by weight PAA (according to EC/10/2011 regulation on plastic materials and articles intended to come into contact with food), even when using PU prepolymer without additional hardener.

Regarding the migrating surface, the following amounts (in μg/dm ² ) of the migrating solution at 70° C. for 0 hours were determined.

2,6-TDA 2,4-TDA 4,4'-MDA 2,4'-MDA 2,2'-MDA 0.32 <0.15 <0.15 <0.15 <0.18

Embodiment 2 (comparative example)

44 parts of polyester PE 230 were dissolved in 9.25 parts of ethyl acetate and then reacted at 80° C. with 5 parts of 2,4-TDI. Then 29.75 parts of ethyl acetate and 4.5 parts of a mixture of dibutylamine and bis(3-(triethoxysilyl)propyl)amine are added until no more isocyanate groups are present.

To this prepolymer, 7.5 parts of a styrene copolymer containing about 50% by weight of maleic anhydride structural units are added, and the mixture is homogenized. The end product obtained had a viscosity (Brookfield/spindle 3) at 20° C. of 1060 mPa·s and a solids content of 56% by weight.

The prepolymer was then used to laminate different film structures at a dry coat weight of 2.7 g/m ² . Properties were tested as described in Example 1.

Table 4: Properties of printed OPP/OPP ink binders: NC-PU (gravure printed)

color BS – 1 day BS – 14 days BS – 28 days blue 0.58/60% ink transfer 0.47/80% ink transfer 0.42/80% ink transfer blue White 0.98/90% ink transfer 0.49/95% ink transfer 0.22/90% ink transfer White 1.9/50% ink transfer 0.86/95% ink transfer 0.39/100% ink transfer

Table 5: Properties of printed OPP/OPP ink binders: NC-PU (flexo-printed)

color BS – 1 day BS – 14 days BS – 28 days blue 1.09/90% ink transfer 1.25/5% ink transfer 0.74/0% ink transfer blue White 1.15/100% ink transfer 0.96/100% ink transfer 1.18/80% ink transfer White 1.9/0% ink transfer 2.39/coexist tear 1.19/100% ink transfer

Table 6: Properties of printed PET/PE ink binders: PUR (flexo-printed)

color BS – 1 day BS – 14 days BS – 28 days blue 1.3/90% ink transfer 0.96/100% ink transfer 0.66/100% ink transfer blue White 4.21/PET tearing 2.39/PET tear 1.6/90% ink transfer White 3.11/0% ink transfer 0.95/100% ink transfer 1.38/100% ink transfer

Since the adhesive does not contain any residual isocyanate groups, it immediately complies with EC/10/2011. However, it exhibits low adhesive properties.

Embodiment 3 (comparative example)

Mix at a ratio of 20:1 LA 3966-21 (Henkel AG&Co.KGaA; NCO component; solid content: 80% by weight; solvent: ethyl acetate) with hardener LA 6152 (NCO/OH index: 2.13) was used as lamination adhesive at 3.5 g/m ² . Bis(3-(triethoxysilyl)propyl)amine was not used.

None of the laminates showed <10 ppb by weight of PAA immediately after lamination and required more than 24 hours of cure at room temperature to comply with EC/10/2011 regulations.

Properties were tested as described in Example 1.

Table 7: Properties of printed OPP/OPP ink binders: NC-PU (gravure printed)

color BS – 1 day BS – 14 days BS – 28 days blue 2.04/70% ink transfer 2.1/100% ink transfer 1.52/coexist tear blue White 4.24/0% ink transfer 1.76/100% ink transfer 1.33/100% ink transfer White 4.35/0% ink transfer 1.26/100% ink transfer 1.27/coexist tear

Table 8: Properties of printed OPP/OPP ink binders: NC-PU (flexo-printed)

color BS – 1 day BS – 14 days BS – 28 days blue 2.43/coexist tear 3.04/coexist tear 2.45/coexist tear blue White 1.81/0% ink transfer 2.53/coexist tear 2.4/ Coexistence Tear White 1.73/0% ink transfer 2.71/coexist tear 1.03/100% ink transfer

Table 9: Properties of printed PET/PE ink binders: PUR (flexographically printed)

color BS – 1 day BS – 14 days BS – 28 days blue 2.05/0% ink transfer 4.19/PET tearing 3.75/PET tear blue White 2.06/0% ink transfer 2.88/PET tear 1.43/100% ink transfer White 2.22/0% ink transfer 1.29/100% ink transfer 1.22/100% ink transfer

In conclusion, the examples show that only the prepolymer composition according to example 1 exhibits good adhesive properties, also giving laminates which immediately comply with the EC/10/2011 regulations. That is, a residual PAA content of less than 10 ppb by weight is obtained directly after lamination, so that the laminate can be used for food packaging directly after lamination. The prepolymer according to Example 2, even if compliant with instant food regulations, was deficient in adhesive properties. In contrast, the NCO component according to Example 3 provides good adhesive properties, but results in a higher residual PAA content which does not allow the laminate to be used directly after lamination food packaging.

Claims (16)

1. A prepolymer composition comprising at least one polyurethane prepolymer containing free isocyanate groups, said polyurethane prepolymer being obtainable through the following steps: (a) reacting at least one polyol with at least one polyisocyanate, wherein said at least one polyisocyanate is used in an amount such that NCO groups are present in a molar excess relative to the hydroxyl groups of said at least one polyol, to obtaining a polyurethane prepolymer containing free isocyanate groups; and (b) adding at least one compound with at least one H-acidic functional group to the polyurethane prepolymer containing free isocyanate groups in step (a), in an amount such that the free isocyanate groups and the H-acidic functional group The molar ratio (NCO:XH ratio) is 2-15, preferably 2.5-10, more preferably 3-8. 2. The prepolymer composition of claim 1, wherein said at least one compound having at least one H-acidic functional group (a) comprising at least one primary amino group, secondary amino group, mercapto group, carboxyl group, hydroxyl group or acidic C-H group as said at least one H-acidic function, in particular comprising at least one primary amino group, secondary amino group or mercapto group; and/or (b) has only one H-acidic function. 3. The prepolymer composition according to claim 1 or 2, wherein said at least one compound having at least one H-acidic function comprises at least one silane group. 4. The prepolymer composition of claim 3, wherein said at least one compound having at least one H-acidic functional group is a silane of formula (I): ((R ² ) _m (R ¹ O) _3-m Si-alkyl) _o Nu (I) in Nu is NH, _NH2 , SH, COOH or OH, preferably NH, _NH2 or SH, more preferably NH or SH, most preferably NH; R _{is selected from H and C 1-20} ^alkyl , preferably C _1-4 alkyl, more preferably methyl and ethyl; R ² is selected from C _1-4 alkyl, preferably methyl and ethyl; m is 0, 1 or 2, preferably 0 or 1, more preferably 0; "alkyl" is linear or branched C _1-6 alkylene or C _3-6 cycloalkylene, preferably -(CH ₂ ) _n -, wherein n is an integer of 1-6, preferably 1-4, More preferably 1, 2 or 3; and Wherein, o is 1 if Nu is NH ₂ , SH or OH, and o is 2 if Nu is NH. 5. The prepolymer composition of claim 4, wherein said at least one compound having at least one H-acidic functional group is an aminosilane selected from the group consisting of 3-aminopropyltrimethoxysilane ( AMMO), 3-aminopropyltriethoxysilane (AMEO), 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl base)-3-aminopropyltrimethoxysilane (DAMO), N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-amino Propylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N,N-bis(2-aminoethyl)-3-aminopropyl Trimethoxysilane, N,N-bis(2-aminoethyl)-3-aminopropyltriethoxysilane, N,N-bis(2-aminoethyl)-3-aminopropylmethyl Dimethoxysilane, N,N-bis(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-N'-(2-aminoethyl base)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-N'-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2- Aminoethyl)-N'-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-N'-(2-aminoethyl)- 3-aminopropylmethyldiethoxysilane, bis(triethoxysilylpropyl)amine, bis(trimethoxysilylpropyl)amine, N-(2-aminobutyl)- 3-aminopropyltriethoxysilane, N-(2-aminobutyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, N - (n-butyl)-3-aminopropyltriethoxysilane, and mixtures thereof. 6. The prepolymer composition of any one of claims 1 to 5, wherein step (a) comprises: reacting the at least one polyol with a first diisocyanate and a second diisocyanate, wherein the The first diisocyanate has a first NCO group, the second diisocyanate has a second NCO group, wherein, compared with at least one of the second NCO groups, in the first NCO group At least one of is less reactive toward the hydroxyl groups of the at least one polyol. 7. The prepolymer composition of claim 6, wherein (a) the molar ratio of NCO groups of said first diisocyanate to NCO groups of said second diisocyanate is at least 6:1, preferably at least 10:1, more preferably at least 15:1; and/or (b) the first diisocyanate is an asymmetric diisocyanate, preferably 2,4-TDI; and/or (c) The second diisocyanate is a symmetrical diisocyanate, preferably 4,4'-MDI. 8. The method for preparing the prepolymer composition according to any one of claims 1 to 7, comprising: (a) reacting at least one polyol with at least one polyisocyanate, wherein said at least one polyisocyanate is used in an amount such that NCO groups are present in a molar excess relative to the hydroxyl groups of said at least one polyol, to obtaining a polyurethane prepolymer containing free isocyanate groups; and (b) adding at least one compound having at least one H-acidic functional group to the polyurethane prepolymer containing free isocyanate groups in step (a), in an amount such that the moles of free isocyanate groups and H-acidic functional groups The ratio (NCO:XH ratio) is 2-15, preferably 2.5-10, more preferably 3-8. 9. Adhesive composition comprising the prepolymer composition according to any one of claims 1 to 7, optionally also comprising at least one tackifier, catalyst, stabilizer, crosslinking agent, viscosity Regulators, fillers, pigments, plasticizers, water scavengers and/or antioxidants. 10. The adhesive composition of claim 9, wherein the composition further comprises at least one polymer having anhydride functionality, preferably a maleic anhydride copolymer or a maleic anhydride grafted polymer. 11. A method of bonding two or more substrates selected from the group consisting of plastic surface articles, metals, fabrics, paper and cardboard, the method comprising: (a) applying the adhesive composition according to claim 9 or 10 to the surface of at least one substrate to be bonded, alone or in admixture with a hardener, preferably comprising a compound selected from the group consisting of hydroxyl, H-acidic functional groups of primary amino, secondary amino, mercapto or carboxyl groups; and (b) contacting the surfaces of the substrates to be bonded with the adhesive composition therebetween under conditions suitable to form an adhesive bond between the substrates; (c) optionally repeating steps (a) and (b); Wherein the hardening agent preferably comprises an H-acidic functional group selected from hydroxyl, primary or secondary amino, mercapto or carboxyl; more preferably a polyol component; most preferably a polyol containing two or more hydroxyl groups per molecule components. 12. The method according to claim 11, wherein at least one, preferably two or more, of the two or more substrates are film-like substrates. 13. Multilayer laminate obtainable by the method according to claim 12. 14. The multilayer laminate of claim 13, wherein the laminate is: (a) a bilayer laminate; and/or (b) Laminates for food packaging applications. 15. Use of the adhesive composition according to claim 9 or 10 as a lamination adhesive, preferably as an adhesive for laminating at least two film-like substrates, more preferably as an adhesive for food Uses of adhesives for packaging applications. 16. Use according to claim 15 for achieving a migration limit of primary aromatic amines of <10 ppb by weight.